Generally, a pressure-sensitive record material is composed of a combination of an upper sheet, on a surface of which are coated a number of pressure-rupturable microcapsules containing a solution of an electron-donative colorless basic dye (color-forming agent), and a lower sheet, on a surface of which is coated an electron-accepting acid material (color-developing agent) capable of developing color images on the lower sheet when in contact with the colorless basic dye. The above-mentioned type of pressure-sensitive record materials are disclosed in U.S. Pat. Nos. 2,730,456 and 2,730,457.
Generally, the color-forming agent is selected from triphenylmethane type color-forming dyes, for example, Crystal Violet lactone (CVL). This type of color-forming agent can produce clear blue-violet images the moment it contacts the acid color-developing agent. However, the thus produced color images exhibit a very poor light fastness to the point that, when exposed to sunlight or ultraviolet rays, the color images rapidly fade within a short time and, finally, disappear. Also, the color images consisting of the triphenylmethane type dye exhibit such a disadvantage that the color images disappear when they contact water during the storage thereof. In order to decrease the above-mentioned disadvantages of the color images, it has been attempted to mix a methylene blue type colorless dye which is capable of producing a color image having a relatively high light fastness into the triphenylmethane type color dye. However, it was found that this cannot eliminate the disadvantages of the triphenylmethane type dye per se. Also, the mixture exhibits such a disadvantage that, during a long period of storage of the color images, the color of the images alters from dark navy blue to light green.
The above-mentioned disadvantages of the conventional pressure-sensitive record material are remarkably exhibited when a solid acid, for example, attapulgite or acid terra alba, is used as a color-developing agent. In order to eliminate the above-mentioned disadvantage of the solid acid, various approaches were attempted.
In one approach, various acid clay type mineral materials, kaolin, and zeolite were treated physically by heat or chemically with an acid or alkali, to provide, for example, activated clay, fired kaolin, and fired activated clay. In another of the approaches, the above-mentioned solid acids were used together with various inorganic compounds, for example: a water-insoluble salt of cobalt, manganese or lead (Japanese Examined Patent Publication No. 41-16822(1966)); a water-soluble salt of zinc, cadmium, mercury, calcium, magnesium, strontium, manganese, cobalt, or nickel (Japanese Examined Patent Publication No. 42-20,143(1967)); a metal hydroxide or carbonate (Japanese Examined Patent Publication No. 41-16,262(1966)); an alkali neutralization product of a hydroclorate or sulfate of aluminum, manganese, or zinc (Japanese Examined Patent Publication No. 43-10,091(1968)); an alkali neutralization product of a hydrochlorate or oxide of tin, zinc, or aluminum (Japanese Examined Patent Publication No. 42-25,250(1967)); a complex of a cupric compound with ammonia (Japanese Examined Patent Publication No. 43-28,431(1968)); a complex of a colloidal zinc hydroxide with water glass (Japanese Examined Patent Publication No. 44-2,193(1969)); a treatment product of zinc oxide with ammonia (Japanese Examined Patent Publication No. 46-9,290(1971)); a metal nitrite (Japanese Examined Patent Publication No. 51-15,777(1976)); a mixture of a rhodanate with a metal compound (Japanese Examined Publication No. 48-12,254(1973)); or a mixture of an organic cyanamide compound with a metal compound (Japanese Examined Patent Publication No. 50-16,968(1975)). In still another approach, microcapsules containing therein a mixture of urea or thiourea, zinc chloride, and a solvent, are used as a color-developing agent (French Pat. No. 2,246,399). In further approaches, there were used as a color-developing agent effective for improving the water fastness and light fastness of the color images, in place of the inorganic color developing agent, such as clay: an organic compound, for example, a phenol compound (U.S. Pat. Nos. 3,244,584, 3,244,549, and 3,244,550); a condensation product of a phenol compound with an aldehyde compound, that is, a novolak resin (British Pat. Nos. 1,053,935 and 1,233,665); or an aromatic carboxylic acid, for example, benzoic acid, naphtoic acid, or salicylic acid, an acid derivative of the carboxylic acid or a metal compound of the carboxylic acid or its acid derivative (Japanese Examined Patent Publications Nos. 49-10,856(1974), 49-13,451(1974), and 52-1,327(1979)). In the other approaches, the above-mentioned organic acid substance was used together with an inorganic color developing agent, such as clay (British Pat. No. 1,065,587), or the above-mentioned inorganic color-developing agent was used together with urea or thiourea, and a chloride of zinc, vanadium, chromium, manganese, iron, cobalt, nickel or copper (British Pat. No. 1,506,813).
However, the above-mentioned approaches failed to provide color images having satisfactory color depth, water fastness and/or light fastness.